Selectively controllable radiant energy device

ABSTRACT

A gaseous discharge device is connected to a suitable source of electrical energy which may typically be of the pulsed DC type to generate the emission of radiant energy having a determinable spectral character. A magnetic field is caused to perpendicularly intercept the electric field resultant from the flow of current through the gaseous discharge device causing a controllable and predictable change in the spectral character of the emitted radiant energy in accordance with the strength of the magnetic field. By increasing the strength of the magnetic field, two or more peaks of radiant energy of different spectral character may be generated so that peak emitted power may be realized within a desired spectral region to be employed as the excitation energy for a laser, for example.

United States Patent Daniel E. Altman;

Myer Geller, both at San Diego, Cnlll. [21] Appl. No. 873,323

{22] Filed Nov. 3, 1969 [45] Patented 5,1971

[73] Assignee The United States 01 Anterlca as represented by theSecretary at the Navy [72] inventors [54] SELECTIVELY CONTROLLAILERADIANT Fork et al., Broodband Magnetic Field Tuning of Optical Mascrs"App Phys. Lett., 2, (9), 1 May 1263 pp, 1 8 9 181 Ahmed et a1., GasLasers in Magnetic Fields," Proc. IEEE 52,(1l), Nov., 1964 pp.1356-1357.

Egorov et al., Some....l'le-Ne Pulse Discharge..." Optics 8:Spectroscopy, )(Vii (4), April I965, pp. 405- 406.

Boss et al., Broodband Light Amplification in Organic Dyes, App. Phys.Lett., 11, (3), 1 Aug. 67, pp. 89- 9 1.

Primary Examiner-Ronald L. Wibert Assistant Examiner-R. J. WebsterAttorneys-.1. C. Warfield, .Ir., George J. Rubens and John W.

McLaren AISTRACT: A gaseous discharge device is connected to a suitablesource of electrical energy which may typically be of the pulsed DC typeto generate the emission of radiant energy having a determinablespectral character. A magnetic field is caused to perpendicularlyintercept the electric field resultant from the flow of current throughthe gaseous discharge device causing a controllable and predictablechange in the spectral character of the emitted radiant energy inaccordance with the strength of the magnetic field. By increasing thestrength of the magnetic field, two or more peaks of radiant energy ofdifferent spectral character may be generated so that peak emitted powermay be realized within a desired spectral region to be employed as theexcitation energy for a laser, for example.

SELECTIVE! ONTGLLA$ELEZ nnumu'r ENEEG! DiEt/lliCl'd BACKGROUND (IF THEiNVfiNTlON Numerous sources of excitation energy are employed in theloser for epic, and many different kinds of gaseous disch devices havebeen used. Customarily, different 3 will produce peak power outputs ofradiant energy at different bandwidths in accordance with the gasuelcctcd. lfn gas in itelectcd which produces a peel: power output ofrmiant energy within the spectral bandwidth which may be usuallyemployed to excite a particular laser material to lasing level, anacceptable degree of efficiency of power transfer may be realized bymatching the selected us discharge device for use with that particularlaser material.

However, in typical work with laeers and laser materials it has beenfound that each different laser material will require peak power at edifiercnt spectral bandwidth which is charactcristic of that particularlesser material. Accordingly, it is customary that one particularexcitation source is selected from many different possible sources ofexcitation energy to be employed with each different laser material inan effort to effect a most efficient power transfer from the excitationsource to the lasing material. Generally, this is so because of the fastthat it is relatively moot difficult to control the radiation spectrumemitted by excitation eourcee such as gaseous discharge devices.

It is possible to change the constituent within the gaseour dischargedevice, to change its pressure, or to even change the geometry of theeloctrodw employed and the configuration of the discharge vessel; it isalso possible to change the amount of electrical current flowing throughthe gaseous discharge device in order to effect tome control over theradiation spectrum emitted by the gas. However, all of those ofexercising n limited degree of control over the radintion spectrum ofthe energy emitted by the gas are relatively difficult, cumbcrnome, timeconsuming, and involve a comparatively mayor operation on one or moreparameters of the dioclmrge device lmelf.

Moreover, when a change hen been completed, such an altering theconstinsent gen, its pressure, the geometry of the elcctrodco, or thedischarge vessel, or variably controlling the electrical current throughthe r discharge device, the changed or modified radiation in which willthen be emitted by the us discharge device is not recdily changeable tothe orim'nal radiation spectrum. in other words, such limitedmodifications and controls as may be effected by altering one of theeters, geometries, or constituents as mentioned hereinbeforc is in thenature of a permanent change which does not readily adept itself tobeing returned to its original or another alternative mode of operation.The nature of such change requires a concomitant change back to itsoriginal condition in order to return the us discharge device to a modeof operation which will produce its ordinal output, if that should bedesired. Accordingly, there exists a need for a source of radiant energywhich can be controllably changed to generate peak power radiant energyof a dificrent mctral character within a bandwidth of interest and yetbe readily returned to its normal emimlon of radiant energy of apredetermined spectral character without further alteration of thephysical character or principal parameters of the device.

SUMMARY OF THE INVENTION The present invention contemplates thegeneration of radient energy of reversal controllably different spectralemissions. in its most fundamental form the present invention maycomprire a r um discharge device such or Xenon lamp or other suitablegas discharge flash lamp which is connected to :1 source of electricalenergy for producing a flow of current through the gas in order togenerate the omission of radiant energy when rained to an appropriateenergy level. Typically, many ouch gaseous discharge dcvioea may beenergized by pulsed direct current which devclope a pulsating flow ofcurrent through the pea, cnuslnp it to omit radiant energy of adeterminable spectral character.

There are many materials available, particularly dye liquids, whichwould provide excellent possibilities for efi'rcient and powerful lasersif the materials could be sufficiently excited by radiant energy withintheir absorption bonds. Generally, however, the emission spectrum 'ofXenon gnu discharge lamp, for instance, does not overlap the absorptionspectrum of such dye liquid material and consequently they cannot beconveniently and efficiently energized to sufficient enerw levels tocause them to achieve the lasing phenomenon. The present invention,however, teaches the use of a magnetic field positioned perpendicularlyto the direction of the electric field which is resultant from the flowof current in a gaseous discharge device, to thereby controllably changethe spectral character of the emitted radiant energy. As a result, avery distinct and marked change is effected in the normal and usual peakradiant energy output of n gnaeous discharge device, affordingsignificantly greater latitude in the effort to match the spectralcharacter of the peak power output of the radiant energy emitted by thegaseous discharge device to coincide with the abeorption band of thematerial which it is desired to raise to a lasing energy level.

For example, it has been found that a gaseous discharge devicecontaining nitrogen may have its penlt bands of spectral emissionsignificantly changed by the application of an appropriate magneticfield as taught by the concept of the present invention. In the presenceof a weak or no magnetic field the nitrogen will be found to emit peakenergy at approximately 4,340 A. Upon the application of a magneticfield, however, the same nitrogen gas discharge device will emit peakenergies at approximately 4,450 A. and 4,430 A. Thus, the peak energiesemitted by the gaseous discharge device have been significantly changedin spectral character so that the same gaseous discharge device may beemployed by encrgizc laser materials which absorb in the 4,450 A. to4,430 A spectral band.

Accordingly, it is a primary object of the present invention to providea source of radiant energy which may be controllably operated to emitdifferent spectral bands of peak energy.

it is an equally important object of the present invention to providesuch a source of controllebly different spectral peak energy by theemployment of a magnetic field which permits the device to return to itsnormal spectral character of radiant energy upon removal of the magneticfield.

Another important object of the prcecnt invention is to provide a sourceof radiant energy which may be controllably altered to match theabsorption band of a lmr material.

Yet another most important object of the present invention is to providea means by which the radiant energy generated by a laser material may becontrollably altered in spectre! character.

A further object of the present invention is to provide a means by whichthe spectral character of emitted radiant energy may be controllablychanged to any one of several selectable spectral hands by the changeand control of a magnetic field employed as taught by the presentinvention.

These and other features, objects, and advantages of the presentinvention will be better appreciated from an understanding of theoperative principles of a preferred embodiment as deacribod hereinafterand as illustrated in the accompenying drawings.

BRIEF DESCRIPTION OF THE DRAWlNGS DESCEllPTlON OF THE PREFERREDEhlllODlMENT in FIG. 3 the gaceour discharge device 210, such as n Xenonlamp or a suitable cavity filled with nitrogen, for example, ispositioned in the airpap of a substuntielly U-ahaped member offerromagnetic material ill. in the embodiment of HG. l, two coils H2 andH3, tively, are wound about portions of the ferromagnetic material llproximate to the nirgap. The coils B2 and no may be serially connectedto each other Md also to a source of electrical encrw lid to cuuwcurrent to flow through the coils and develop a strong magnetic field inthe uirgap as a function of the current flow.

Another source of electrical energy R5 in provided to be connectcd tothe gaseous discharge device lid to cause current to flow thercthroughand to generate emieuion of rudiunt energy. in the preferred embodimentof the present invention as illustrated in FIG. l, u luwr cell necemblylb may be positioned close to the radiant energy source it) so no toreceive the emitted power radiated therefrom. it may be desirable toenclose both the source of radiant energy, in the form of a gaseousdischarge device 20, and the laser assembly id (or at similar device)within a common internally reflective enclosure l7 so that the maximumamount of radiant energy emitted from the gaseous dicchargc device i0 iscaused to impinge upon and be absorbed by the laser or similar deviceto.

the gaseous ditchargc device 10 and the laser or similar device which itis desired to stimulate with emitted radiation, may be convenientlyarranged to be removable and replaceable in the assembly illuetrated inFIG. 1. Accordingly, a different laser assembly may be substituted inthe position of element H6 as illustrated in H6. 1 as may be desired toeffect efi'zcieut ahcorption of certain spectral peak radiated poweremanating from the gaseous discharge device id. in an malcgous mannerthe gaseous discharge device l0 may be replaced turd have substitutedtherefor a gaseous discharge device of differing operativecharacteristics to provide a means of generating peak radiant powerwithin certain other spectral bands as may be desired to give effect tooptimum spectral matching; for the most efficient power transfer asbetween the radiated energy and the power absorbed by the illlifi'l. lb,or a similar device.

PEG. 2 in an end view illustrating the disposition of the severalelements of the preferred embodiment shown perspectively iu PEG. 5. Likeelements mourn in H6. 2 have the wine numerical designations as in FIG.i. it will be noted that the gaseous discharge device 10 is clearlydisposed at the center of the airgap formed by the substantiallyU--shnped element ll of ferromagnetic material. This arrangement ispreferred in order that the gaseous discharge device l0 intercept themagnetic field of grcateut strength and highest intensity. Element llmay be formed of a number of pieces of ferromagnetic material as desiredand convenient in fabrication. For exampic, as illustrated by the endview of FlG. 2, a first U-shaped element lllc is supplemented by likeelements llb and lie disposed on opposite sides of the basic element Naand secured thereto by appropriate means euch as the bolts l8 and H0. ltwill be noted, as clearly shown in the illustration of FIG. 2, that thelaser or similar device to, which is contained within an internallyreflective enclosure R7 together with the gaseous discharge device i0,is disposed so an to be outside the area of maximum intensity ofmagnetic field strength. This is usually desirable and particularly sowhere element lie is a laser and it is desircable not to disturb thenormal, predictable operation of the laser by causing it to be exposedto too high an intensity of magnetic field.

It is to be understood, of course, as will be readily apparent to thoseskilled and knowledgeable in the art, that the particular configurationillustrated in lFlGS. l and 2 is only one of many possible forms of thepresent invention and that the concept and teaching disclosed herein maybe widely and varicurly employed as desired to effect desirable results.

o en/mom In a typical operation of the embodiment illustrated in H68. 11and 2 the gaseous discharge device 10 may be, for example, a nitrogengas lump energized by a source of electrical energy lfi which is pulsedDC in nature. The coils of conductive material 32 and ill may beenergized by an independent source of electrical energy M which isdirect current in nature. Accordingly, the electric field created by theflow of electrical current through the gaseous discharge device i0 is inthe come direction as the current flow. The magnetic field, however,which traverses the eirgup of the ferromagnetic element ill isunidirectional and perpendicular to the electric field.

When thc gaseous discharge device lid is energized by the source ofdirect current electrical energy E5 in the absence of an electric field,the nitrogen gas will emit radiant energy having a spectral charactergenerally of that shown by the solid line characteristic illustrated in,lFlG. 3, depicting intensity of radiation versus Angstrom units'. Itwill be neon that it major peak of radiant energy output occurs atapproximately 4,340 A., with a relatively minor peak bf radiant energyoutput in the vicinity of 4,415 A. It has been found that substantiallythe smile spectral character of rudiiant energy output will be realizedin the absence of any magnetic field as in the presence of a weakresidual magnetic field such as may remain in an electromagneticconfiguration of the type illustrated in FIGS. 11 and 2 after the sourceof electrical energy to the coils has been disconnected. The residualelectric field in one such typical embodiment was found to be of theorder of 600 gauss.

Upon energizing the coils l2 and ill, the intensity of the magneticfield traversing the airgnp of the ferromagnetic ele ment ll is raisedto approximately 20,000 gauss, affecting a dramatic change in the outputof peak radiant energy emitted from the some nitrogen gas lamp whosenormal characteristic is illustrated by the solid line graphicalillustration in H6. 3. As shown in FIG. 3 by the dashlinccharacteristic, peak energy outputs of radiant energy from the gaseousdischarge device in the form of a nitrogen flash lump are caused tooccur at approximately 4,344 A., 4,433 A., and 433%! A., the principalcal; energy output occurring at the latter frequency.

Thus, it may be seen that where a dye liquid, for example, may requireenergy in an abwrption band at or near 45147-48 A, a nitrogen gas lampenergized by an appropriate pulsed DC source of electrical energy andpositioned in a magnetic field of the order of 20,000 gauss can becaused to emit peak energy in the required spectral band. Those skilledand knowledgeable in the art will appreciate that the example given of anitrogen gas lamp will operate without a magnetic field or with anegligible residual field to produce spectral emission typical of thenitrogen molecule. With a magnetic field, however, the molecular bandsare radically changed to a degree where they virtually disappear and thespectral emis- :sion of ionized atomic nitrogen becomes prominent, thelatter spectral emission arising from a much more highly energizeddischarge. One interpretation of this effect may be that with a magneticfield, more energy can be fed into the gas with a resultant increase inthe electron temperature i.e., the average electron energy which canexcite the molecule to a higher energy state, disaseocioting themolecule, ionizing the atom, and aloe exciting the ion. Thus, thepresent invention conceives and teaches the control of radiation from agaseous discharge device in a convenient, efficient and readilypracticublc manner.

it should also be appreciated that the gaseous discharge device 20 maybe a laser device itself so that the concept and teaching of the presentinvention is equally as readily applicable to altering the emissioncharacteristics of a laser directly, as well as altering the emissioncharacteristics ofn device used m an excitation source for a laser whichin turn is positioned proximate to the gaseous discharge device.

Moreover, it hast been found that, within the teaching and concept ofthe present invention, it is possible to change the magnetic fieldstrength and intensity in several degrees, achieving several diiierentdistinctive spectral emission characteristics, each of which differsfrom the other as a result of different intensities of magnetic fieldsapplied to the gaseous discharge device.

The mamietic field, as employed in the present invention may be providedby an appropriate permanent magnet, an electromawet or other suitablearrangement consistent with the inherent requisites for the practice ofthe invention.

Obviomly many modifications and variations of the present invention arepomible in the light of the above teachings. It is therefore to heunderstood that within the scope of the ap pended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

5. Means for generating radiant energy having controllably differentspectral emissions comprising:

a gaseous discharge device including a gas enclosed within an envelope;

a source of electrical energy connected to said gaseous discharge devicefor producing a flow of current therethrough generating the emission ofradiant energy of a determinable spectral character;

a magnetic field source for generating a magnetic field; and

means for positioning said magnetic field source relative to saidgaseous discharge device for causing the magnetic field toperpendicularly intercept the electric field resultant from said flow ofcurrent, the intensities of said magnetic field source and saidelectrical energy being of such amplitudes as to raise said gaseousdischarge device to a higher state of ionization for producing spectralemis sion which is characteristic of said higher state of ionizatron.

2. Means for generating radiant energy as claimed in claim 1 whereinsaid gaseous discharge device is capable of emitting laser energy.

3. Means for generating radiant energy as claimed in claim I whereinsaid source of electrical energy is pulsed direct current.

4. Means for generating radiant energy as claimed in claim I whereinsaid magnetic field source is a permanent magnet.

5. Means for generating radiant energy as claimed in claim I whereinsaid magnetic field source is an electromagnet.

6. Means for generating radiant energy as claimed in claim 5 whereinsaid electromagnet is controlled by a variable source of electricalenergy, whereby to selectively change the spectral character of theemitted energy to one of several spectral regions each of which ischaracteristic of a different state of ionimtion.

7. Means for generating radiant energy as claimed in claim l andincluding a laser material optically coupled with said gaseous dischargedevice for pumping of said laser material.

8. Means for generating radiant energy as claimed in claim 7 whereinsaid laser material is highly absorptive of energy of the spectralcharacter of the radiant energy emitted at said higher state ofionization.

9. Means for generating radiant energy as claimed in claim 7 whereinsaid laser material is positioned with its principal axis parallel tothe principal axis of the gaseous discharge device and substantiallycoextensive therewith.

10. Means for generating radiant energy as claimed in claim 8 whereinsaid laser material is positioned to be subjected to the minimumstrength of magnetic field.

1!. Means for generating radiant energy as claimed in claim 9 whereinsaid laser material and said gaseous discharge device are containedwithin a common internally reflective laser pump enclosure.

1. Means for generating radiant energy having controllably differentspectral emissions comprising: a gaseous discharge device including agas enclosed within an envelope; a source of electrical energy connectedto said gaseous discharge device for producing a flow of currenttherethrough generating the emission of radiant energy of a determinablespectral character; a magnetic field source for generating a magneticfield; and means for positioning said magnetic field source relative tosaid gaseous discharge device for causing the magnetic field toperpendicularly intercept the elEctric field resultant from said flow ofcurrent, the intensities of said magnetic field source and saidelectrical energy being of such amplitudes as to raise said gaseousdischarge device to a higher state of ionization for producing spectralemission which is characteristic of said higher state of ionization. 2.Means for generating radiant energy as claimed in claim 1 wherein saidgaseous discharge device is capable of emitting laser energy.
 3. Meansfor generating radiant energy as claimed in claim 1 wherein said sourceof electrical energy is pulsed direct current.
 4. Means for generatingradiant energy as claimed in claim 1 wherein said magnetic field sourceis a permanent magnet.
 5. Means for generating radiant energy as claimedin claim 1 wherein said magnetic field source is an electromagnet. 6.Means for generating radiant energy as claimed in claim 5 wherein saidelectromagnet is controlled by a variable source of electrical energy,whereby to selectively change the spectral character of the emittedenergy to one of several spectral regions each of which ischaracteristic of a different state of ionization.
 7. Means forgenerating radiant energy as claimed in claim 1 and including a lasermaterial optically coupled with said gaseous discharge device forpumping of said laser material.
 8. Means for generating radiant energyas claimed in claim 7 wherein said laser material is highly absorptiveof energy of the spectral character of the radiant energy emitted atsaid higher state of ionization.
 9. Means for generating radiant energyas claimed in claim 7 wherein said laser material is positioned with itsprincipal axis parallel to the principal axis of the gaseous dischargedevice and substantially coextensive therewith.
 10. Means for generatingradiant energy as claimed in claim 8 wherein said laser material ispositioned to be subjected to the minimum strength of magnetic field.11. Means for generating radiant energy as claimed in claim 9 whereinsaid laser material and said gaseous discharge device are containedwithin a common internally reflective laser pump enclosure.